1. Field of the Invention
The present invention relates to an actuator, and particularly relates to an actuator that is installed in a digital camera, mobile phone, or other compact precision apparatus and drives a zoom lens and a focusing lens.
2. Description of the Related Art
As a driving device for a lens unit of a digital camera, etc., an actuator that employs a piezoelectric element is used. For example, an actuator of JP-A-2002-142470 is arranged from a piezoelectric element, a driving member, and a pedestal. The driving member is affixed to one end face along an extension/contraction direction of the piezoelectric element, and a drive member is frictionally engaged with this driving member. The pedestal is affixed to the other end face along the extension/contraction direction of the piezoelectric element. This pedestal functions as a weight member that is an inertial body, and with this arrangement, pulse-form voltages are applied to the piezoelectric element and movements of the piezoelectric element in an extension direction and a contraction direction are transmitted by the inertial action of the pedestal to the driving member. When the piezoelectric element deforms at a low speed, the driven member moves along with the driving member, and when the piezoelectric element deforms at a high speed, the driven member stays at the same position due to its mass inertia. Thus, by repeatedly applying pulse-form voltages, the driven member can be moved intermittently at a fine pitch.
With the actuator arranged as described above, there is an issue that resonance occurs among the pedestal, the piezoelectric element, and the driving member. With the actuator of JP-A-2002-142470, to prevent the effects of resonance when the actuator is mounted onto a main body, the pedestal is affixed to the main body by a rubber-based adhesive agent to elastically support the actuator on the main body. However, with such a drive system, scattering of the arrangement of the pedestal, the piezoelectric element, and the driving member becomes extremely difficult to control.
When such resonance is made use of, the merit of increased moving amount of the driving member is provided. For example, an actuator that makes use of this resonance is described in Japanese Patent No. 3171187. With this actuator, by applying pulse-form voltages in accordance to the displacement of the piezoelectric element during resonance, the displacement amount of the driven member is made large.
However, with the actuators of JP-A-2002-142470 and Japanese Patent No. 3171187, when the weight of the pedestal that functions as a weight member is small, even when the resonance is made use of, the moving distance, moving speed, and thrust of the driven member is inadequate. Although a pedestal of large weight is thus required, this makes the device large. In particular, in a case where a zoom lens or other driven member of large moving distance is to be moved, a pedestal of extremely large weight is required and the device becomes large.
Also, with the actuators of JP-A-2002-142470 and Japanese Patent No. 3171187, because the resonance state, which arises in the actuator arranged from the piezoelectric element, the driving member, and the pedestal, is made use of, the inadvertent effects of the resonance are applied and the driven member becomes displaced in directions besides the extension/contraction direction of the piezoelectric element. For example, a driving member 2 receives the influence of the resonance and becomes displaced in directions besides the extension/contraction direction of a piezoelectric element as shown in FIGS. 5A and 5B. The driving force due to extension/contraction of the piezoelectric element 1 is thus not accurately transmitted to a driven member 3, and the driven member 3 cannot be moved accurately in the extension/contraction direction of the piezoelectric element 1.